Deniz Yucel, who has both Turkish and German citizenship, was detained on February 14 after his reports about a hacker attack on the email account of Turkey's energy minister, Die Welt newspaper said.

Yucel was questioned by a prosecutor in Istanbul on Monday for three hours before a judge ordered him formally arrested pending the preparation of an indictment and a trial. Die Welt confirmed that he was ordered into custody.

Yucel, 43, joins scores of journalists who have been jailed in Turkey following a July 15 coup attempt that prompted a government crackdown on alleged anti-government activists. This has included the closure of at least 100 news outlets in Turkey.

The private Dogan news agency said Yucel was also questioned about an interview he conducted with Cemil Bayik, a commander of the outlawed Kurdistan Workers' Party (PKK) , as well as about articles he had written on Turkey's policies towards the Kurds .

Activists in Berlin demonstrated against Yucel's detention by projecting #FreeDeniz on the Turkish embassy building in the German capital.

The Die Welt journalist was asked whether he had any links to the hacker collective RedHack, which obtained the energy minister's emails that were made available on WikiLeaks, Dogan reported. The energy minister, Berat Albayrak, is President Recep Tayyip Erdogan's son-in-law.

Festival director Dieter Kosslick protested Yucel's detention at the award ceremony of the 67th annual Berlin International Film Festival [EPA]

Germany's foreign ministry said last week that Yucel's case was of "greatest importance" for Berlin and that it would do "everything in our power to support press freedom" in Turkey.

In a statement, Germany's Chancellor Angela Merkel criticised the move as "bitter and disappointing" and called it "disproportionate".

"The German government expects that the Turkish judiciary, in its treatment of the Yucel case, takes account of the high value of freedom of the press for every democratic society. We will continue to insist on a fair and legal treatment of Deniz Yucel and hope that he will soon regain his freedom," she said.

There had been protests in Berlin following Yucel's detention two weeks ago and on February 19, Festival director Dieter Kosslick closed the award ceremony of the 67th annual Berlin International Film Festival by raising his fist into the air in honour Yucel in front of a photograph of him.